PBH dark matter spans all naturalness tiers, with some mechanisms as natural as WIMPs or freeze-in particles, determined by abundance map structure rather than candidate type.
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Adiabatic CMB perturbations in pre-big bang string cosmology
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abstract
We consider the pre-big bang scenario with a massive axion field which starts to dominate energy density when oscillating in an instanton-induced potential and subsequently reheats the universe as it decays into photons, thus creating adiabatic CMB perturbations. We find that the fluctuations in the axion field can give rise to a nearly flat spectrum of adiabatic perturbations with a spectral tilt $\Delta n$ in the range $-0.1 \lesssim \Delta n \lesssim 1$.
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Lattice simulations directly calculate SIGW spectra with non-Gaussianity to all orders and show that modest non-Gaussianity alters ultraviolet spectral behavior.
Curvaton self-interactions in non-quadratic potentials produce a local non-Gaussian map that enables supermassive primordial black hole formation at peak amplitudes of order 10^{-5} while remaining consistent with μ-distortion bounds.
First UVLF-based constraints on model-agnostic isocurvature power spectra for CDM, baryon, neutrino, and dark radiation modes yield consistent 95% credible envelopes over k ~ 0.5-10 Mpc^{-1}.
Stochastic effects in multifield inflation make the number of fields relevant for e-fold statistics and power spectrum, with a general formula for higher moments and an upper bound on fields for successful inflation.
A light axion spectator induces post-inflation tachyonic phases that produce a nearly scale-invariant boost to the curvature power spectrum and alter key inflationary observables in a largely potential-independent manner.
A spectator scalar in modulated reheating with large Higgs-like couplings generates detectable scalar-induced stochastic gravitational waves for BBO and DECIGO, but only outside perturbative low-energy extrapolations.
Including spectral running α_s, β_s and self-interacting dark radiation relaxes the ACT DR6 bound on ΔN_eff to <0.58 and lowers the Hubble tension to 2.2σ with three extra parameters.
A spectator scalar field with strong portal coupling to the inflaton sources a stochastic gravitational wave background reaching Ω_GW h² ∼ 10^{-11} at frequencies 10^7-10^8 Hz for benchmark parameters σ/λ ≃ 10^4 and T_reh = 2×10^{14} GeV.
A tutorial deriving cosmological perturbation equations from inflation through reheating, with explicit gauge-invariant computations and Python scripts.
Lecture notes providing an advanced introduction to primordial inflation theory and perturbation theory in slow-roll and quasi-de Sitter spacetimes.
citing papers explorer
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Are Primordial Black Holes a Natural Dark Matter Candidate?
PBH dark matter spans all naturalness tiers, with some mechanisms as natural as WIMPs or freeze-in particles, determined by abundance map structure rather than candidate type.
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Scalar-induced gravitational waves with non-Gaussianity up to all orders
Lattice simulations directly calculate SIGW spectra with non-Gaussianity to all orders and show that modest non-Gaussianity alters ultraviolet spectral behavior.
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Memoirs of the curvaton: non-perturbative non-Gaussianity and supermassive primordial black holes
Curvaton self-interactions in non-quadratic potentials produce a local non-Gaussian map that enables supermassive primordial black hole formation at peak amplitudes of order 10^{-5} while remaining consistent with μ-distortion bounds.
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New Isocurvature Constraints from JWST UV Luminosity Function
First UVLF-based constraints on model-agnostic isocurvature power spectra for CDM, baryon, neutrino, and dark radiation modes yield consistent 95% credible envelopes over k ~ 0.5-10 Mpc^{-1}.
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Multifield stochastic inflation: Relevance of number of fields in statistical moments
Stochastic effects in multifield inflation make the number of fields relevant for e-fold statistics and power spectrum, with a general formula for higher moments and an upper bound on fields for successful inflation.
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Tachyonic Encore: A universal shift of inflationary observables
A light axion spectator induces post-inflation tachyonic phases that produce a nearly scale-invariant boost to the curvature power spectrum and alter key inflationary observables in a largely potential-independent manner.
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Stochastic Gravitational Waves from Modulated Reheating
A spectator scalar in modulated reheating with large Higgs-like couplings generates detectable scalar-induced stochastic gravitational waves for BBO and DECIGO, but only outside perturbative low-energy extrapolations.
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The End of the First Act: Spectral Running, Interacting Dark Radiation, and the Hubble Tension in Light of ACT DR6 Data
Including spectral running α_s, β_s and self-interacting dark radiation relaxes the ACT DR6 bound on ΔN_eff to <0.58 and lowers the Hubble tension to 2.2σ with three extra parameters.
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Gravitational Waves from Matter Perturbations of Spectator Scalar Fields
A spectator scalar field with strong portal coupling to the inflaton sources a stochastic gravitational wave background reaching Ω_GW h² ∼ 10^{-11} at frequencies 10^7-10^8 Hz for benchmark parameters σ/λ ≃ 10^4 and T_reh = 2×10^{14} GeV.
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From inflation to hot big bang -- a tutorial on cosmological perturbations
A tutorial deriving cosmological perturbation equations from inflation through reheating, with explicit gauge-invariant computations and Python scripts.
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Three Advanced Lectures on Inflation
Lecture notes providing an advanced introduction to primordial inflation theory and perturbation theory in slow-roll and quasi-de Sitter spacetimes.